Process antifoams



page

ates Fatent @fi Patented E eh. 19, 1963 The present invention is directed to methods and compositions for controlling the foaming tendencies of aqueous solutions under various conditions. The invention has particular applicability to the control of foaming in the generation of steam from boiler water under various conditions of pressure.

The present invention is directed to the prevention of foaming, or its control, by the addition of materials to an aqueous system to prevent initiation of foaming conditions and also to the introduction of the compounds into a system already foaming for the purpose of destroy: ing or controlling the foaming condition. I

The problems encountered under conditions of boiling under atmospheric pressure, sub-atmospheric pressure, and super-atmospheric pressure may be considerably different insofar as the selection of a suitable anti-foam agent is concerned. Some materials have little or no anti-foam activity at atmospheric pressure or sub-atmospheric pressure, but become extremely effective antifoams when the boiler is operated at a super-atmospheric pressure. Conversely, some materials are effective antifoam agents at low pressures but lose their efiec-tiveness when the steam generating system is operated at elevated pressures. With the compositions employed in the practice of the present invention, however, one can select particular compositions for particular pressure conditions and thereby provide an anti-foam which is tailor made for the particular environment.

An object of the present invention is to provide an improved method for controlling or inhibiting foam formation in aqueous systems having a tendency to foam.

Another object of the invention is to provide an improved method for destroying existing foaming conditions in aqueous systems.

A further object of the invention is to provide a method for controlling foaming conditions in aqueous systems operating to generate steam under various pressure conditions.

A further obiect of the invention is to provide an improved s'elf-emulsifiable anti-foam composition for combating foaming tendencies in steam generating systems.

In the practice of the present invention, I employ, as the effective anti-foam agent, a polyoxypropylene addition product of a trihydroxy substituted propane having the empirical formula:

where n is either 3 or 6.

One class of compounds coming under this definition consists of 1, 2, 3 polyoxypropylene glycerols having the following formula:

Compounds of the type illustrated in the foregoing formula commence exhibiting anti-foam activity at a mini mum molecular weight of about 1000, and particularly efifective in materials at molecular weights within the range of 1000 to 5000. These addition products are sold commercially by the Dow Chemical Company under the designation Polyglycol 11. The representative members of this group of compounds are given in the following table:

Another class of materials which fall within the class definition are the polyoxypropylene derivatives of trimethylolpropane having the structural formula:

In this type of compound, foam inhibiting efiectiveness seems to occur at a minimum molecular weight of 400, and the preferred compounds have molecular weights of from 400 to 5000.

The applicability of the materials as foam destroyers under atmospheric boiling conditions was determined in the following manner. The liquid under test was admitted to a large Pyrex tube and kept at a constant level within the tube by using an inverted flask filled With distilled water. The material was heated by an electrical heating element operating at a constant voltage. The heating element was turned on and the liquid was heated for 40 minutes to reach the constant maximum foam height. Testing material was then added to the boiling liquid. The liquid was heated for another 5 minutes to assure uniform distribution of the testing material within the liquid. The height of foam produced Was then measured during a period of 5 minutes. The foam height was recorded as a difference between the average height attained by the liquid plus foam and the original height of the liquid. A slightly alkaline feed water having a pH of 11.0 was used in the test. The following table compares the results obtained from the various compounds employed in the present invention:

The foam controlling efi'ectiveness of these compounds is even further increased when they are combined with a relatively minor amount of a quaternary ammonium salt having at least 1 hydrocarbon chain containing at least 12 carbon atoms. This efiiect is particularly surprising since the quaternary salts themselves have little foam inhibiting capability. Suitable quaternary'salts for the practice of this invention include materials such as Arquad 2C (di-coconut dimethyl ammonium chloride), Arquad T (mono-tallow trimethyl ammonium chloride) and Arquad O (mono-octadecenyl trimethyl ammonium chloride). These salts, when added in a mixture with the foam inhibiting material to the extent of 5 to 20% of the mixture provide a self-emulsifiable composition which is quite stable.

Under the same conditions of anti-foam testing mentioned previously, the following results were obtained:

Height of foam produced in mm. at specified time intervals While the composition illustrated in the foregoing table is very efiective as an anti-foam at atmospheric pressure, when elevated pressures are to be encountered, it is advisable to use a polyoxypropylene glycerol having a higher molecular weight. Particularly good results have been obtained by using the combination of Polyglycol 11-200 in an amount of 90%, combined with of Arquad 2C (75% active). This particular composition evidenced an anti foam life of 11 minutes and 8 seconds at a dosage of 0.2 part per million in a test boiler operating at 200 pounds per square inch gauge pressure and a temperature of 390 F.

Industrial water treating systems which operate under sub-atmospheric pressures such as evaporators and vacuum distillation processes present special problems from the standpoint of foaming. Stability of the antifoam composition is of particular importance in this use. The compositions of the present invention can also be employed in sub-atmospheric pressure systems with good results. For this type of application, I prefer to employ the combination of the polyoxypropyiene glycerol and a polyethylene glycol ester of an organic acid containing at least 12 carbon atoms per molecule. The molecular weight of the polyethylene glycol may range from about 200 to 2000 although a value of about 400 is preferred. When the polyethylene glycol esters are added in amounts from about 5 to of the composition, a self-emulsifiable mixture results which has excellent stability characteristics.

The foam destroying tendencies of various compositions of the present invention, and the foam inhibiting properties of the compositions under sub-atmospheric pressure conditions are listed in the following tables:

Foam heit'lit produced in mm,

measured after boiling for spec- Doslied intervals (pressure of 100 Additive are, mm. in boiler. heating element peroperating at 100 volts) cent 10 15 20 25 30 Min. Min. Min. Min. Min.

1,255 165 170 130 140 165 Poly,,- ycol 11400 90%, 1

quad 2O Active),

10 0 0. 037 125 220 0 440 Po1yglyco111300 0.037 150 105 100 75 75 Polyglycol 11-300 Arquad 2C (75% Active),

10, 0.037 125 210 300 425 Polyslycol ll-l00 0.037 87 92 90 95 9 Polyglycol 0%. Ar-

10 U 0.037 72 155 210 315 Polyglycol 11-400 90%.

Polyethylene glycol 400 monooleate.10% 0.037 80 90 S5 97 Dosage levels employed will vary, of course, depend ing upon the severity of the foaming condition. However, as a general rule, it is advisable to add at least one part per million of the active ingredient up to about 500 parts per million both for purposes of foam destiuction and foam inhibition. Larger amounts can be added, if desired, but generally are not required and are therefore not economical.

While the compositions of the present invention have particular utility in the prevention of foaming under conditions of boiling, they can also be employed to advantage in the treatment of other aqueous systems to inhibit, con trol, or destroy foam. One such application exists in the field of foaming ore flotation where the flotation water is recirculated rapidly in order to conserve water. Compositions of the present invention do not interfere with the production of the controlled foam necessary for ore flotation but are successful in destroying the foam after it leaves the flotation vats.

The compositions of the present invention also find use in'other processes wherefoaming is a problem, particular- -ly in the paper making industry for the treatment of paper producing stocks.

It will be evident that various modifications can be made to the described embodiment without departing from the scope of the present invention.

I claim as my invention:

1. A self-emulsiiiable anti-foam composition consisting essentially of a mixture of polyoxypropylene glycerol raving a molecular weight of at least 1000 and a quaternary ammonium salt having at least one hydrocarbon chain of at least 12 carbon atoms, said salt being present in an amount of from 5 to 20% by weight of said mixture.

2. A self-emulsitiable anti-foam composition consisting essentially of a mixture of a 1,2,3 polyoxypropylene glycerol having a molecular weight of from 1000 to 5090 and a quaternary ammonium salt having at least one hydrocarbon chain of at least 12 carbon atoms, said salt being present in an amount of from 5 to 20% by weight of said mixture.

3. The method of inhibiting foam formation in a system having a tendency to team on boiling which con prises dispersing into said system a mixture of at least one part per million of a 1,2,3 polyoxypropyiene glycerol having a molecular weight from 1000 to 5000 and a quaternary ammonium salt having at least one hydrocarbon chain of at least 12 carbon atoms, said salt being added in an amount of from 5 to 26% by weight of said mixture.

References Cited in the file of this patent UNITED STATES PATENTS Schnell et a1 Apr. 12, 1955 Jursich Dec. 13, 1955 Chappell June 25, 1957 Johnson Feb. 24, 1959 FOREIGN PATENTS Great Britain Feb. 13, 1957 

1. SELF-EMULSIFIABLE ANTI-FOAM COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF POLYOXYPROPYLENE GLCEROL HAVING A MOLECULAR WEIGHT OF AT LEAST 1000 AND A QUARTERNARY AMMONIUM SALT HAVING AT LEAST ONE HYDROCARBON CHAIN OF AT LEAST 12 CARBON ATOMS, SAID SALT BEING PRESENT IN AN AMOUNT OF FROM 5 TO 20% BY WEIGHT OF SAID MIXTURE. 